The components of a chain saw in general, including the chain saw pruner contemplated for the present invention, typically include a loop of saw chain consisting of interconnected links (wire sections shaped into links) having cutting teeth (e.g., a sharpened end of the wire link). An elongate planar element termed a guide bar or blade supports and guides the saw-chain loop in a peripheral groove of the bar, the loop is driven in rapid rotation around the guide bar by a sprocket disposed at one end of the bar and mounted on a chain saw housing to which the blade is attached. The sprocket is coupled to an output shaft of the power head of the chain saw.
Proper tension of the saw chain must be established and maintained so that the chain will track smoothly around the guide bar and over teeth of the sprocket without binding, and without excessive looseness, which could cause undesirable vibrations of the chain or even cause the chain to become untracked from the guide bar.
The guide bar of the conventional high-powered chain saw is adapted to be slidably movable longitudinally with respect to the sprocket to permit adjustment in the tension of the saw chain from time to time as the chain wears. The adjustment generally is effected by manual means such as a threaded member having an element bearing longitudinally upon the guide bar.
The advent of chain saw pruners has made the manual adjustment of saw chain tension more difficult because the range of variation of movement permitted to establish proper chain tension diminishes substantially in smaller chain saws. For example, a small chain saw with a saw-chain loop less than fourteen centimeters (5-1/2 inches) long and 4.5 centimeters (1-3/4 inches) wide may require an adjustment in relative distance between the guide bar and the sprocket of as little as 0.150 millimeter (0.006 inch). This can make the difference between a tight chain that consumes the power of the motor needed to drive the chain for cutting, and a free running chain that permits the power of the motor to be applied to the desired cutting action.